How to teach and think about spontaneous wave function collapse theories: not like before

TL;DR

This paper offers a straightforward way to understand spontaneous wave function collapse theories by connecting them to standard quantum measurement concepts, highlighting that only the master equations are empirically testable.

Contribution

It introduces a simple, textbook-based approach to spontaneous collapse, clarifying the role of noise and emphasizing the empirical relevance of master equations over stochastic Schrödinger equations.

Findings

Noise in collapse models originates from standard quantum measurement concepts.

Master equations of the noise-averaged state are the only empirically testable dynamics.

Stochastic Schrödinger equations are empirically redundant.

Abstract

A simple and natural introduction to the concept and formalism of spontaneous wave function collapse can and should be based on textbook knowledge of standard quantum state collapse and monitoring. This approach explains the origin of noise driving the paradigmatic stochastic Schr\"odinger equations of spontaneous localization of the wave function $\Psi$. It reveals, on the other hand, that these equations are empirically redundant and the master equations of the noise-averaged state $\hat\rho$ are the only empirically testable dynamics in current spontaneous collapse theories.